You can use brightness controller , it's not accurate , but provides you tweaking the rgb
Install Brightness Controller with the following commands:
sudo add-apt-repository ppa:apandada1/brightness-controller
sudo apt update
This does not make your brightness function keys work, but is a workaround.
Install Brightness Controller with the following commands:
sudo add-apt-repository ppa:apandada1/brightness-controller
sudo apt update
For Version 2 with Multi Monitor Support and Color Temperature support:
sudo apt install brightness-controller